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It is well known that the performance (definition irrelevant) of 2 developers (definition irrelevant) of identical educational background and industry experience can vary by as much as 1000%.
This is because software development is in many way a form of art, and Google are basically holding "auditions" for a part in their software development performance.
This is exactly how it should be. You don't hire an actor based on a CV and an interview.
(no i'm not entering by the way!)